1. Field of the Invention
The present invention relates to a waveguide-transmission line transition for converting electrical power in a microwave or millimeter-wave band.
2. Description of the Related Art
Japanese Patent Application Laid-Open (kokai) No. 10-126114 (Feeder Transition) discloses a known type of waveguide-transmission.line transition capable of effecting mutual conversion between power transmitted through a waveguide and power transmitted through a strip line.
FIG. 22 is a.perspective view of a waveguide-transmission line transition 300 according to a prior art technique; FIG. 23A and 23C are cross-sectional views of the transition 300; and FIG. 23B is a plan view of the transition 300.
A strip line 3 is provided on one surface of a dielectric substrate 4, and a grounding metal layer 5xe2x80x94which is to be connected to an opening surface of a waveguide 2xe2x80x94is provided on the other surface of the dielectric substrate 4. The dielectric substrate 4 is fixedly sandwiched between a short-circuiting waveguide block 9 and the waveguide 2. Since a high efficiency of the transition is obtained when the strip line 3 is disposed at a position within the waveguide 2 at which a strong electric field is present, the distance between the short-circuiting surface of the short-circuiting waveguide block 9 and the strip line 3 is set to about xc2xc of the wavelength x in the waveguide.
When the conventional transition 300 is used to connect the waveguide 2 to a microwave or millimeter-wave circuit, the short-circuiting waveguide block 9 vertically projects from a substrate on which microwave or millimeter-wave circuit is formed, because the strip line. 3 is located on the same plane as that of the substrate of the microwave or millimeter-wave circuit. Especially, when such a transition is used for conversion in a microwave band, the height of the projection (xcex/4) of the short-circuiting waveguide block 9 sometimes exceeds 2 cm, which hinders miniaturization of the microwave circuit.
Meanwhile, when the conventional transition is used for conversion in a millimeter wave band, the matching characteristics of the transition 300 deteriorate when a slight positional shift is produced among the waveguide 2, the short-circuiting waveguide block 9, and the strip line 3. Therefore, in order to obtain a high efficiency of the transition, the waveguide 2, the short-circuiting waveguide block 9, and the strip line 3 must be fixed with positional accuracy as high as about {fraction (1/100)} mm.
However, the above-described conventional structure makes it difficult to fix the short-circuiting waveguide block 9 and the waveguide 2, among other components, with such high accuracy, and therefore has been a main cause of hindering mass production of waveguide-transmission line transitions.
The present invention was accomplished in order to solve the above-described problems, and an object of the present invention is to provide a waveguide-transmission line transition which has a high efficiency of the transition and a reduced size, and which can easily be produced on a large scale.
Another object of the present invention is to provide a waveguide-transmission line transition having a structure which prevents variation (deterioration) of properties such as a resonant frequency, which would otherwise occur due to variation in waveguide width among mass-produced waveguides.
According to a first aspect of the present invention, there is provided a waveguide-transmission line transition which includes a strip line projecting inward on an opening surface of a waveguide to be parallel to the opening surface and which effects mutual conversion between power transmitted through the waveguide and power transmitted through the strip line, comprising a plate-shaped short-circuiting member shielding the opening surface of the waveguide and having a slit in which the strip line is disposed; a matching element disposed within the waveguide, the matching element being substantially parallel to and separated by a predetermined distance from the short-circuiting member; and a dielectric member disposed between the short-circuiting member and the matching element, wherein the strip line disposed in the slit and the matching element are disposed in proximity to each other to be electromagnetically coupled.
According to a second aspect of the present invention, as is concretely shown in a first embodiment, the short-circuiting member is a short-circuiting plate having a slit in which the strip line is disposed; and the dielectric member comprises at least a first dielectric substrate which is inserted into the slit and which has the strip line disposed on its outer surface.
According to a third aspect of the present invention, the transition according to the second aspect is further characterized in that the dielectric member comprises a second dielectric substrate which is joined to reverse surfaces of the short-circuiting plate and the first dielectric substrate and on which the matching element is formed.
According to a fourth aspect of the present invention, as is concretely shown in a second embodiment, the dielectric member is formed of a first dielectric substrate shielding the opening surface of the waveguide and a second dielectric substrate which is joined to a reverse surface of the first dielectric substrate and on which the matching element is formed; and the short-circuiting member is formed of a short-circuiting metal layer formed on an outer surface of the first dielectric substrate and having a slit, wherein the strip line is disposed in the slit of the short-circuiting metal layer.
According to a fifth aspect of the present invention, as is concretely shown in a third embodiment, the dielectric member is formed of a dielectric substrate which shields the opening surface of the waveguide and which has the matching element on its reverse surface; and the short-circuiting member is formed of a short-circuiting metal layer formed on an outer surface of the dielectric substrate and having a slit, wherein the strip line is disposed in the slit of the short-circuiting metal layer.
According to a sixth aspect of the present invention, the dielectric substrate or the first dielectric substrate has on its reverse surface, opposite the surface where the strip line is formed, a grounding metal layer which comes into contact with an end face of a side wall at the opening surface of the waveguide.
According to a seventh aspect of the present invention, the short-circuiting metal layer and the grounding metal layer are electrically connected with each other by means of through-holes.
According to an eighth aspect of the present invention, the strip line is disposed in each of a plurality of slits formed in the short-circuiting member.
According to a ninth aspect of the present invention, the grounding metal layer is formed and disposed such that a region surrounded by an inner circumference of the grounding metal layer on the reverse surface of the second dielectric substrate or the dielectric substrate is completely included in a region surrounded by an inner wall of the waveguide.
According to a tenth aspect of the present invention, the center of the matching element is offset from the center of the waveguide by a predetermined distance xcex94 along the longitudinal direction of the strip line toward the direction of projection of the strip line.
According to an eleventh aspect of the present invention, the predetermined distance xcex94 falls within a range of about 1 to 4% the narrower wall-to-wall distance P of the waveguide.
According to a twelfth aspect of the present invention, at least two through-holes are disposed on opposite sides of an entrance of the slit; and the distance between the through-holes is less than double the width of the strip line.
According to a thirteenth aspect of the present invention, impedance adjustment is performed through adjustment of a length over which the strip line overlaps with the matching element.
According to a fourteenth aspect of the present invention, resonant frequency adjustment is performed through adjustment of the length of the matching element along a direction parallel to the strip line.
According to a fifteenth aspect of the present invention, the distance between the strip line and the matching element falls within a range of 0.01 to 0.20 xcexg, where xcexg is a wavelength within the dielectric member existing between the strip line and the matching element.
According to a sixteenth aspect of the present invention, the distance between the strip line and the short-circuiting metal plate or layer falls within a range of 0.03 to 0.06 xcexg, where xcexg is a wavelength within a medium existing between the strip line and the short-circuiting metal plate or layer.
According to a seventeenth aspect of the present invention, the dielectric member on which the strip line is provided is formed integrally with a circuit substrate on which a microwave or millimeter-wave circuit is formed.
According to an eighteenth aspect of the present, invention, the first dielectric substrate and the second dielectric substrate are formed integrally.
According to a nineteenth aspect of the present invention, a second grounding metal layer is formed at a peripheral portion of the second dielectric substrate such that the second.grounding metal layer is in contact with the side wall of the waveguide.
The second grounding metal layer may be formed of the same metal layer as that of the above-described first grounding metal layer. Therefore, a metal layer which concurrently meets the requirements of the first and second metal layers may sometimes be referred to as a xe2x80x9cgrounding metal layerxe2x80x9d without distinguishing them.
The above-described waveguide-transmission line transition can solve the problems involved in conventional waveguide-transmission line transitions.
In the waveguide-transmission line transition according to the present invention, the strip line disposed in the slit of the short-circuiting metal plate or layer is disposed in close proximity to the matching element to establish electromagnetic coupling, i.e., capacitive coupling, therewith, so that power conversion is effected by the electromagnetic coupling between the strip line and the matching element. Accordingly, a short-circuiting waveguide block which has been indispensable in the conventional waveguide-transmission line transitionxe2x80x94can be omitted. Therefore, there can be eliminated the above-described projection which projects about xcex/4 from the substrate surface of a microwave or millimeter-wave circuit, to thereby enable flattening of (rendering compact) the waveguide-transmission line transition.
Further, since the short-circuiting waveguide block is eliminated, an operation for precise relative positioning between the short-circuiting waveguide block and the waveguide, accompanied by xcex/4 restriction, becomes unnecessary, so that production of the waveguide-transmission line transition is facilitated.
Moreover, in the waveguide-transmission line transition according to the present invention, impedance matching is effected through adjustment of the length of insertion of the strip line into the waveguide. Further, a frequency band in which transmission and conversion are performed can be determined through adjustment of the size of the matching element and the distance between the strip line and the matching element.
When the width of the matching element as.measured along the longitudinal direction of the cross section of the waveguide is large, the frequency band becomes broader. In addition, the width of the matching element as measured along a direction perpendicular to the longitudinal direction determines the cut-off frequency. Further, the width of the frequency band changes with the distance between the matching element and the strip line (the thickness of a dielectric substrate interposed therebetween).
Accordingly, through proper adjustment of these parameters, there can be obtained a waveguide-transmission line transition whose loss at a desired frequency is reduced.
Since the grounding metal layer is provided, the dielectric substrate on which the strip line is provided can be easily and reliably fixed to the waveguide. Therefore, a waveguide-transmission line transition of reduced power loss can be obtained.
When a conductive material such as metal is embedded in through-holes formed in the dielectric substrate, it becomes possible to reliably maintain the short-circuiting metal layer and the waveguide at the same potential. Therefore, a waveguide-transmission line transition of reduced power loss can be obtained.
Since the inner dimension of the grounding metal layer is made smaller than the inner dimension of the waveguide, the distance between the matching element and the conductor (grounding metal layer) formed on the same surface can be maintained constant even when the width of the waveguide varies during mass production. Accordingly, electromagnetic fields produced between the matching element and the grounding metal layer hardly change, so that variation in resonant frequency can be suppressed.
That is, the accuracy of the waveguide width of a waveguide produced through metal working is a few tens of, microns to a few hundreds of microns. By contrast, the accuracy of the strip line formed on the dielectric substrate can be decreased to ten microns or less. Therefore, according to the present invention, deterioration in characteristics due to production errors can be reduced, as compared with the structure in which the resonant frequency changes depending on the width of the waveguide.
In the present invention, the positional relationship between the waveguide and the dielectric substrate is not determined such that the centers of the waveguide and the dielectric substrate coincide with each other, but is determined such that the dielectric substrate is located in the vicinity of the center of a region in which the conversion loss is small. Therefore, the conversion loss does not increase very much even when a positional shift is produced therebetween.
In the present invention, since the distance between two through-holes sandwiching a planar transmission line is sufficiently small, the ratio of power which leaks from the gap between the two through-holes (from an area in the vicinity of the entrance of the slit of the short-circuiting metal layer), i.e., the ratio of the power loss to the total power transmitted from the transmission line to the waveguide, can be reduced.
In the present invention, the distance between the short-circuiting metal layer and the matching element can be increased through provision of the first and second dielectric substrates therebetween. Thus, a frequency band in which power transmission and conversion are performed can be broadened.
In the present invention, the second grounding metal layerxe2x80x94which is provided on the surface of the second dielectric substrate on which the matching element is formedxe2x80x94enables to broaden a frequency band in which power transmission and conversion are performed and to prevent variation (deterioration) of properties of a resonant frequency even when variation occurs in waveguide width among waveguides.